Method and apparatus for accumulating, storing, and releasing thermal energy and humidity

ABSTRACT

A method and apparatus for supplying heat and humidity to gas filled spaces by the addition of water to a dehydrated material that releases heat upon exposure to water, exposing the hydrated material to dry contacting gas which results in loss of water from the hydrated material to the contacting gas, the contacting gas being heated and humidified by such exposure, and subsequent dispersal of the added heat and humidity to the gas filled space. This sequence also results in regeneration of the dehydrated material so that these steps may be repeated. By limiting the amount of water addition to the dehydrated material within a cycle of the process, less time and/or energy is required to regenerate the dehydrated material and finer control of resultant living space humidity may be possible.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to energy collection and distribution and more particularly to improved methods and apparatus for accumulation, storage and controlled release of thermal energy.

2. Description of Related Art

In recognition of the ecological and cost impact of fossil fuels and other conventional energy sources, significant effort has been expended in developing and optimizing sources of energy that are more environmentally benign, including solar, wind, and geothermal energy sources. While these sources show considerable promise in helping to meet future energy needs, significant problems prevent more effective utilization of these types of energy sources.

One problem inherent to these types of sources relates to the timing and location of energy supply and demand. With energy sources such as solar, wind, and geothermal sources, the relative rates of energy supply and demand are not readily matched in terms of time and/or location. For example, for those living above certain degrees of latitude in parts of the northern or southern hemispheres, solar energy collection is not practical year-round and higher rates of energy are typically generated when energy demands themselves tend to be at lower levels. Wind energy is often limited by timing considerations; while wind energy can occur any time of day or any season, it is not controllable either in terms of timing or intensity. As with solar energy systems, many geothermal energy systems are similarly constrained by location considerations. So called “low temperature” geothermal energy systems still require proximity to extremely high temperature resources such as geologically hot rocks and hot springs which are often limited to areas near tectonic plate boundaries. Thus, there is a need for an economical means of storing the energy for effective utilization of energy sources in which the rates of energy supply and demand, timing, and location, are not generally well matched. Also, there is a need for economical and efficient means of utilizing energy sources that are well matched to the time and location of their use. In addition, there are also advantages to systems that can take advantage of waste energy from combustion or other sources.

A number of methods used for heat storage apply energy to increase the temperature of a medium, typically to high temperature levels that exceed acceptable levels for safe direct use and for human or animal contact, and maintain that elevated temperature until the stored heat can subsequently be used. With some approaches to the problem, only short-term storage is feasible, such as using sufficiently large water reservoirs with correspondingly costly insulation for energy storage. With solar collection, special and therefore costly solar collectors can be used if long-term storage is required, since in this case the high temperatures usually encountered are considered necessary for regeneration of the storage medium. In addition, regeneration of such a long-term store is in practice only possible in the summer months with strong direct solar radiation, so that the storage medium must have capacity that extends through the months in which heating is used.

Various chemical storage media have also been proposed for storing and releasing energy using hydration/dehydration cycles and similar techniques at high temperature. While such methods may provide large amounts of thermal energy for subsequent use, the regeneration of the storage medium also consumes large amounts of energy, amounts that may be difficult to obtain from the most desirable sources, particularly for use in low temperature conditions. High amounts of stored heat can also be generated from the storage media when releasing the stored energy, although it is generally at temperatures in excess of what is generally considered to be safe and comfortable for habitable spaces, for example. Thus, current practice often requires the use of heavily-insulated containers or conduits, which are expensive and can result in large losses of heat energy even during short periods of storage or distribution. Because of high levels for generated heat, current methods of heat storage can also require a good measure of isolation between the storage location and the location of use by occupants of a home, workplace, or other facility.

Goals for improved methods and apparatus for accumulating, storing, and releasing thermal energy for living quarters, work environments, and other habitation include the following:

-   -   (i) Capability for energy accumulation and storage at moderate         temperatures. Energy storage using lower temperatures would         enable storage to be accomplished with less time between energy         storage and use in addition to offering reduced risk of scalding         or other injury to nearby inhabitants. This also allows for use         of higher relative humidity source gas for energy storage.     -   (ii) Capability for reversible cycles of energy storage and         release. This relates to overall cost of operation by decreasing         heat requirements for energy storage and/or increasing the speed         of energy storage, environmental impact, and usability.     -   (iii) Capability for self-regulation with respect to         temperatures reached by the storage medium in each cycle. It is         beneficial for controlling the rate at which heat is generated         to be inherently limited by the materials used. This provides         greater flexibility in the delivery of heat in a safe manner, as         well as providing a control on the amount of humidity provided.     -   (iv) Capability for providing controlled added humidity. The         level of ambient humidity can affect the relative comfort level         of a house, workplace, or other habitation at a particular         temperature. In addition, when appropriately controlled, ambient         humidity can have health benefits and preserve the integrity of         building components and contents that are susceptible to damage         under low or high humidity conditions. Also, a higher level of         relative humidity allows lower temperatures to be more         acceptable and more comfortable for building occupants during         the heating season, for example. At the same time, it is         desirable to control the humidity level even during the heating         season to avoid condensation on cold surfaces such as windows         and creating environments conducive for undesirable organisms.         Therefore, it is also beneficial to limit the amount of added         humidity. In addition, it is desirable to add humidity during         the heating season without the cooling effect that can occur         upon water evaporation.     -   (v) Environmentally benign. It would be advantageous for any         type of storage material or system to use components that are         not toxic, not detrimental to the environment and do not undergo         chemical transformation upon exposure to components of living         environments such as air and water.     -   (vi) Capable of locating the energy generation and energy         storage components in the same place, without requiring that         energy storage be provided at a separate facility or location.         At the same time, it would be advantageous to also provide a         solution that allows storage of energy to be performed at a         location that is different from locations where energy is         released.     -   (vii) Low cost and complexity. The storage system should require         as little added energy as possible for heaters, compressors,         pumps, and other equipment requiring large amounts of external         power. In addition, the high cost of such complex equipment         would be undesirable.

A number of solutions have been proposed for energy storage and release using dehydration and hydration of metal salts. However, none of these solutions appears to satisfy the requirements listed in (i) to (vii) above.

For example, U.S. Pat. No. 4,303,121 entitled “Energy Storage by Salt Hydration” to Pangborn describes storage of solar energy or waste heat for later use using endothermic/exothermic cycles of dehydration/hydration of inorganic salts. The Pangborn '121 solution, however, is intended for and describes only high heat and high temperature applications and falls short of what is needed for goals (i), (iii), and (iv).

U.S. Pat. No. 4,291,755 entitled “Method and Apparatus for Accumulating, Storing, and Releasing Thermal Energy and Humidity” to Minto describes a heat storage system that employs polyvalent metal salts to generate heat that is used for drying grain. However, embodiments described in Minto '755 utilize compressed steam and heated oil in hydration and dehydration, providing a system that handles high temperatures, failing to satisfy (i) above, risks uncontrolled temperature elevation and heat evolution, failing to satisfy (iii) above, introducing some environmental concerns relative to (v) above, and not compatible with goal (vi) above. The efficiency of such a system is questionable, making it difficult to satisfy goal (vii) above.

U.S. Pat. No. 4,484,617 entitled “Method of Using and Storing Energy from the Environment” to Sizmann describes heat storage using materials such as silica gel or zeolite, with applied water vapor for heat generation. However, some method of vapor generation must be included as part of the system, making it difficult to satisfy goal (i) above and along with large complex equipment, falling short of meeting goal (vii) above.

U.S. Pat. No. 4,179,493 entitled “Dehydration Process” to Sadan describes the production of dehydrated or anhydrous salts from higher hydrates of the same salt using solar energy. However, embodiments described in Sadan '493 utilize aqueous solutions and a solar pond to obtain the dehydrated or anhydrous salts failing to satisfy (ii) above since no energy release is performed and would require complex separation equipment to obtain the potentiated material for energy release, failing to satisfy (vii) above. In addition, (iv) and (vi) above are not satisfied as humidification cannot be controlled nor can energy generation and storage be co-located or conveniently moved.

Other solutions such as that described in U.S. Published Patent Application 2009/0020264 entitled “Method of Heat Accumulation and Heat Accumulation System” to Morita, and references therein, involve formation of and storage of liquid salt solution phases and require the use of complex and costly equipment such as vacuum pumps and compressors, thereby failing to satisfy (iv) and (vii) above.

SUMMARY OF THE INVENTION

In embodiments of the present invention, thermal energy is stored in a medium which can be maintained in a relatively high potential energy state for indefinitely long periods of time in uninsulated or partially insulated containers, and can be controllably liberated at another time or another place, while also being able to be used at or near the same location and used very shortly after storage of the energy, and the heat storage medium thereafter recharged or reactivated by the application of heat and/or dry air to the medium.

The invention provides an improved method of accumulating, storing and controllably releasing thermal energy with a storage medium at moderate temperatures in the 10-75° C. range and wherein the medium can be indefinitely recycled by regenerating the medium.

The invention uses a process that is self-regulating with respect to the maximum temperature reached by the medium. Apparatus of the present invention can be used to store energy from a range of sources including solar, wind, hydroelectric, nuclear, wave and geothermal energy. Additionally, energy sources from other processes, such as waste heat from a furnace or furnace ducts, oven, stove, clothes dryer, washer or fireplace, or waste engine heat may be used.

The present invention supplies heat and humidity to gas filled spaces by the addition of water to a dehydrated material that releases heat upon exposure to water, exposing the hydrated material to dry contacting gas which results in loss of water from the hydrated material to the contacting gas, the contacting gas being heated and humidified by such exposure, and subsequent dispersal of the added heat and humidity to the gas filled space. This sequence also results in regeneration of the dehydrated material so that these steps may be repeated. By limiting the total amount of water addition to the dehydrated material within a cycle of the process, less time and/or energy is required to regenerate the dehydrated material and finer control of resultant living space humidity may be possible.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a concept diagram that shows the cycle of hydration and dehydration.

FIG. 2 is a graph that compares temperature and mass percentage of material for energy storage using the method of the present invention and a prior art approach.

FIGS. 3A to 3C are schematic diagrams showing components of a system for thermal energy storage and release.

FIGS. 4 a-4 d are schematic diagrams showing variations for providing outside air in exemplary embodiments of the present invention.

FIG. 5 is a schematic diagram showing parts of an alternate embodiment of a system for thermal energy storage and release.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that elements not specifically shown or described herein may take various forms well known to those skilled in the art. Figures provided herein are given to show overall function, operation, and relationships and are not drawn with the intention of showing components or elements to scale.

Various terms are used in the art to describe the process by which energy can be stored using materials that exhibit heat of hydration. In the context of the present disclosure, the term “dehydration” is used for the storage process and is considered to be essentially equivalent to the terms “regeneration” or “potentiation” that are sometimes used in the art.

Embodiments of the present invention utilize dry air or other type of dry gas as the gas that contacts hydrated material in order to perform dehydration. By “dry gas” is generally meant a contacting gas having sufficiently low moisture content to effect drying when it moves past a material that is at least partially hydrated. Roughly speaking, such dry gas should have a moisture content of less than about 10 grams per cubic meter and preferably less than about 6 grams per cubic meter. The less moisture content, that is, the lower the water vapor pressure, the faster the drying. As is well known, moisture content is a factor in determining relative humidity (RH), along with temperature.

The “equilibrium phase transition temperature” for salt hydrates is defined as the temperature at and above which a salt hydrate releases water such that a liquid phase forms under equilibrium conditions. The present invention, which operates at least partially under the non-equilibrium condition of low water vapor pressure above the salt during dehydration, enables dehydration to occur at temperatures at or below the equilibrium phase transition temperature.

Embodiments of the present invention contemplate an improved method and apparatus of handling thermal energy in which a metal salt or mixture of metal salts having different states of hydration, is utilized as a heat storage medium.

The sequence diagram of FIG. 1 shows the cycle of steps used in embodiments of the present invention. Heat is generated in a hydration step 10, in which water 14 is added to a heat storage medium 12 to effect hydration of the medium and generate heat that is removed and applied to its desired use. In an energy storage step 20, the heat storage medium 12 in a low energy, at least partially hydrated state is dried with dry air or other gas 16 to effect dehydration of the storage medium and to separate water of hydration therefrom. Though not shown in FIG. 1, gas 16 may also be used to remove or provide heat at the same time as effecting dehydration. The water of hydration is reversibly removable from the hydrated salt, such as in a stepwise manner, progressing from a higher state of hydration, with lower potential or stored energy, to one or more lower states of hydration, with inversely higher potential energy.

Conventional approaches using heat of hydration, such as those noted above in the Description of Related Art, for example, attempt to maximize heat output. Such an approach, however, also consumes considerable energy in order to store energy for future use. The Inventor, however, has adopted an alternative approach to energy storage, operating over an energy range that neither delivers the peak amounts of heat energy possible from hydration of the material, nor requires higher temperatures and overall energy input for the purpose of storing energy by dehydration. By working over a more moderate energy storage/output range, methods of the present invention can take advantage of lower energy requirements and simpler equipment configurations in order to affect energy storage.

By way of example, the difference between the solutions proposed in the present invention and those taught in the Morita et al. '264 disclosure are illustrated in the comparative graph of FIG. 2. For reference, the energy transition utilized in the Morita et al. '264 method is represented in dashed line form. A hollow circle 90 shows the hydrated state of magnesium sulfate (heptahydrate) with its heat content spent at 20° C. A filled circle 92 shows the dehydrated state of the magnesium sulfate monohydrate in equilibrium with a saturated solution of magnesium sulfate. In order to store energy and move from the hydrated to the dehydrated state using this prior art method, a considerable amount of heat is required, raising the temperature above the phase boundary equilibrium phase transition temperature between the two phases, as shown by a line 94 in the graph.

In contrast, the energy transition used in the present invention does not require this energy input, as shown by a solid line 96 with starred endpoints. As the graph of FIG. 2 shows, the method taught in Morita et al. '264 uses the transition between monohydrate plus saturated solution and heptahydrate forms of the salt medium. By comparison, the method of the present invention operates primarily over the transition between higher levels of hydration, such as empirical compositions of tetrahydrate, pentahydrate and hexahydrate shown in FIG. 2, rather than predominantly monohydrate form obtained by Morita, et al. '264. By doing so, inputting the latent heat necessary for the phase transition to liquid is minimized or avoided. Thus, although the energy output is lower, the amount of energy required for storage is much lower than that of the earlier approach.

For the process used herein, the degree of dehydration that is attainable is a direct function of the temperature to which the salt is subjected and is an inverse function of the partial pressure of water vapor in the fluid (typically air) that is in contact with the salt. The applied fluid can be some other gas than air, for example nitrogen, oxygen, argon, neon, helium or carbon dioxide may be used.

Particularly useful in the dehydration is warming of outdoor air having a temperature below about 20° C. prior to warming. Such warming may occur by methods such as earth-air heat exchange or through the use of another renewable energy source. Similarly, cool indoor air which has gone through warming from a furnace, radiator or other space heating apparatus may also be particularly useful.

During the dehydration, supplemental heat may be applied by a heater or heat from some other source. Preferably, unlike other methods that have been described in the art, such as that taught in the Morita et al. '264 application that require dehydration above the equilibrium phase transition temperature of a hydrated salt, dehydration is done with the temperature of the hydrated salt at or below its equilibrium phase transition temperature in embodiments of the present invention, as was shown with reference to FIG. 2. This helps to minimize energy consumption in the dehydration step and allows for use of permeable materials (e.g., mesh, fabric or yarn) to support the storage medium.

However, the process of the present invention may alternately be used in conjunction with a process in which the storage medium temperature is brought slightly above the equilibrium phase transition temperature during some part of the process and/or utilize vacuum for a portion of the dehydration step. Use of vacuum for the dehydration step may be particularly useful at times when additional humidification of the surroundings or nearby living spaces is not desired. In such a case, it may be possible to increase the rate of dehydration. Once sufficient water is removed, the storage medium temperature may be decreased to at least the equilibrium phase transition temperature and the current inventive process may be continued.

In energy storage step 20 of FIG. 1, water of hydration is extracted from the salt and removed from its presence and the dehydrated storage medium 12 may then be used at or near the same location or stored for later use at or near the same location, or may be stored and/or used at a remote location. The heat potential may be liberated subsequently in a controllable manner by adding water 14 (preferably liquid water) to the dehydrated salt storage medium 12. The temperature at which the heat is liberated from the salt may be a function of the temperature of the storage medium and water, the amount of liquid water 14 added to the salt, the rate at which heat is removed from the medium 12 for use in another process, and the temperature at which the hydrated salt storage medium 12 undergoes a phase transition to the dehydrated salt and saturated solution of the salt.

Referring to FIGS. 3A, 3B and 3C, in accordance with the present invention, the hydrated salt is subjected to the action of a dry contacting gas 16 which acts to sweep away released water vapor 18. The gas that is used as contacting gas 16 may be air, for example. In such a case, the air may even originate from a relatively cold source, such as from outdoor air during the winter that may act as source gas 15. Even though this air may have a high relative humidity (RH) at a lower outdoor temperature, the same air, when heated to room temperature, can serve as dry gas for the function of acting as contacting gas 16.

The contacting gas 16 may optionally be obtained by warming, using heater 44 a, of source gas 15 with naturally derived heat such as from solar energy or geothermal sources, from heat pumps or by waste heat sources, such as suitable flue gas ducts, furnace ducts, ovens, stoves, fireplaces, washing machines, or clothes dryers, or by electric heaters including those whose electricity is derived from solar photovoltaic, wind, hydroelectric, nuclear energy, or stored in electrical batteries, which may be rechargeable or single use, or fuel cells, and may be used directly, or along with any other source of gas.

Alternatively, the source gas 15 may be derived from a storage cylinder of compressed dry gas which may be used either directly without warming or, optionally with application of heat from a heat source, to become the dry contacting gas 16.

This process may be used either in a continuous flow or a batch mode of operation. In a continuous flow operation, the source gas may be dried by causing the gas to contact a strongly hygroscopic or desiccant material (41 in FIG. 4 a) such as anhydrous calcium chloride or anhydrous magnesium chloride prior to contacting the storage medium, while in a batch mode, the gas that is to be used as contacting gas 16 may be dried by simultaneous contact with such strong hygroscopic materials and the storage medium. Additionally, in accordance with the present invention, room air from a living area may be used for at least some part of the dehydration process.

During hydration of the dehydrated material, the total amount of water that is added is limited to that which favorably generates heat with little or no excess liquid solution formed after the water addition. The volume percentage of the water/storage medium mixture that is solid should be greater than 50% following the water addition, preferably it is greater than 90% and most preferably greater than 99%. For the preferred materials, the amount of water added to the dehydrated material should be less than about 60% by weight and often can be less than about 35% by weight.

However, for the most preferred cases, the weight percentage of water added to the dehydrated storage medium 12, such that little or no excess liquid solution forms, is dependent upon the chemical composition of the storage medium and the extent to which it has been dehydrated. Thus, if the dehydrated storage medium has a composition approximating sodium carbonate monohydrate, anhydrous sodium sulfate, sodium tetraborate pentahydrate or magnesium sulfate tetrahydrate, the weight percent of added water to the dehydrated storage medium should most preferably be less than about 50%, 20%, 35%, or 30%, respectively.

Additionally, if too little water is added or if the rate of water addition is too slow, insufficient storage medium heat generation temperature increase is obtained. The minimum weight percent of added water to the dehydrated storage medium should be at least about 5%, preferably at least about 10% and most preferably at least about 15%.

The minimum rate at which water should be added to the dehydrated material is greater than about 0.1 weight percent per second based on the dehydrated material, preferably greater than about 1 weight percent per second based on the dehydrated material, and most preferably greater than about 10 weight percent per second based on the dehydrated material.

It will be understood that where the term “weight percentage” is used herein, what is meant is a weight of water being added as a percentage of the weight of the solid material to which it is being added at that time. Any additional material which is isolated from the material to which the water is being added—whether by having the other material in one or more separate containers, or by isolating the material with some kind of barrier within the same container, such that the added water does not reach the other material—would not be considered when the “weight percentage” was being determined within the teaching of the invention.

The schematic block diagrams of FIGS. 3A, 3B, and 3C show hydration and energy storage steps, respectively, for a thermal energy storage and release system in a gas filled area 30 according to various embodiments of the present invention.

The system is comprised of a storage medium 12 that may be held in trays or otherwise supported by fine wire mesh, fabric or yarn. Furthermore, the storage medium 12 may be free standing or surrounded by a chamber 36 that may be partially thermally insulating and partially thermally conductive or entirely thermally conductive.

A water supply 32 provides water for hydration. Although droplets are shown in FIGS. 3A and 3B, a continuous application or stream of water may also be used. Also, application of water may occur from a water distribution source that provides water from below or within the storage medium. Consistent with an embodiment of the present invention, water is in liquid form, allowing the direct use of tap water or water from a reservoir, water line, or other convenient source. To initiate hydration and release of thermal energy, a valve 34 can be manually or automatically actuated to introduce water into a chamber 36 that contains heat storage medium 12.

As the dashed line indicates, both hydration for releasing energy and dehydration for storing energy can be executed within the same environment 30, such as the same room, building or general area. The use of non-hazardous materials enables the system of the present invention to be used within a habitat, such as a house, office building or workplace, for example. Alternately, using the appropriate support components, hydration for heat generation can be done at one location, with dehydration performed at a different site.

After water addition is completed, source gas 15 can be drawn from outside the area 30 through an outside inlet or conduit 64, or an optional valve 40 can allow drawing some or all of the source gas 15 through an inside inlet 104 within the area 30. A blower 42 draws the gas in, and propels it into the chamber 36 where the dry contacting gas 16 flows across and contacts the material 12. It should be noted that source gas 15 and blower 42 may be replaced by a cylinder of compressed gas and a valve. Preferably, source gas 15 has a temperature of less than about 20° C.

Heat generation can be used to heat the ambient room air surrounding storage medium 12 or to heat another transport medium. In the embodiment shown in FIG. 3A, an optional air duct 100 provides an air path that is in thermal contact with heat storage medium 12 or with chamber 36 for distributing heat due to hydration by routing heated air 110 to the room or other area without having the air 110 pick up humidity 18 from the hydrated material 12. Air duct 100 is particularly useful for diverting the air flow during water addition so that heat may be transferred to the desired location without impacting the water addition. Valve 101 allows control of air flow through the chamber 36 or through the bypass conduit 100, or a mixture of flows.

Dry contacting gas 16 removes moisture from hydrated storage medium 12. The water content of the dry gas increases as it contacts the hydrated form of storage medium 12.

Optionally, a heater 44 a can be provided for heating the source gas 15 to form the dry contacting gas 16, or heater 44 b can be provided for heating the hydrated storage medium 12 which may also cause heating of the source gas 15 and/or dry contacting gas 16.

Water vapor 18 is expelled from chamber 36 to a valve 50 that can direct the output moisture either to an outlet 111 in the same room 30 that contains the thermal energy storage and release system or to a different room, or to the outside 112. One or more optional sensors 46 are used in one embodiment, to sense the humidity of the expelled gas.

Sensor 46 (or a second such humidity sensor) may also be used to measure the relative humidity (RH) of the ambient air in a room or building 30, to determine whether or not to control valve 50 to direct moist gas back into the room or building or expel the moisture to the outside or other room 112 or repeat the method. For example, measuring the water vapor in the heated contacting gas with sensor 46, the water vapor may first increase, then reach a peak value, then decline. When the water vapor level stops declining after it has begun decreasing would provide an indication that the process may be repeated. Alternatively, if it is found that at least 85% of the water added in the hydration step has been removed during dehydration, for example by sensing the weight change of the storage medium, the process may be repeated.

An optional filter 52 helps to inhibit the emission of salt particles into the surrounding environment. Optionally, water vapor expelled during dehydration that is not needed for increasing room humidity is condensed and re-used for subsequent hydration or other use.

FIG. 3B also shows a room temperature and humidity sensor 47, which can be used to control the valves 40, 50, and 101 and blower 42. The sensor 47 may be in wired or wireless communication with the valves and/or blower such that when room humidity and/or temperature level are at various levels relative to a desired set point, the valves and blower may be adjusted to allow for:

-   -   a) heating only of room air, obtained by actuating valve 101 to         direct inlet air 15 through bypass conduit 100 and 110 into the         room 30. Valve 50 could be set in this mode to exhaust         contacting gas 16 to the outside 112.     -   b) heating and humidifying room air, obtained by operating valve         101 to direct inlet air 15 to contact the storage medium 12         directly and setting valve 50 to output contacting gas 111 to         the desired room 30.     -   c) heating only by contact of room air with exterior of chamber         36, obtained by closing valves and/or turning off the blower.

The operation of both valves 50 and 101 could also be set, if desired, to allow a blend of contacting gas 111 and heated bypass air 110 to flow into the room 30 in modes a or b, above. Valve 40 could be set in modes a or b to allow some or all of the intake air 15 to be drawn from the room 30.

Dry air serves as the drying agent in one embodiment of the present invention. The air that is in communication with blower 42 or other type of air mover may be obtained in any of several ways.

FIGS. 4 a to 4 d show a number of options for providing air that is at suitable temperature and humidity levels.

In FIG. 4 a, an air input subsystem 60 receives outside air as source gas 15 directly through a conduit 64, shown being directed through a wall 62 into the habitable area or other room that contains storage medium 12. Conduit 64 may be insulated and may optionally pass through a window or door, for example. A desiccant material canister 41 can optionally be put in the conduit 64 line to dry the air 15 before use.

As shown in FIGS. 4 b-4 d, air input subsystems 68, 70, and 78 use geothermal energy, or some other readily available heat source, to heat the outside air 15, then directs the air through, within, or past wall 62 into the room or other habitable area. Geothermal energy is obtained, for example, by routing the incoming air conduit 64 to a sufficient depth into the earth 76. Conduit 64 may be insulated, especially downstream of the buried horizontal run, The air does not necessarily need to be heated further and can be used at relatively low temperatures, such as temperatures of at least about 10 to 15° C. in some cases.

The rate of dehydration and consequent energy storage is a function of both the temperature and relative humidity of the dry contacting gas 16. Advantageously, embodiments of the present invention do not require extreme temperatures in order to provide energy storage, but can efficiently store energy even using dry air as the source gas at temperatures that are at or below room temperature. In one embodiment, shown as air input subsystem 60 in FIG. 4 a, valve 40 is set to draw ambient air 115 through input 104 from within the room or other habitable area is itself used as input for dehydrating heat storage medium 12.

The schematic diagram of FIG. 5 shows an embodiment in which air input 81 and output 83 are near a window 80. Weather-stripping 82 and insulation 84 are provided, with tubing extending through the insulation 84. Again, heater 44 a is optional, but can be useful for decreasing the relative humidity of the drying air. An optional condensation tank 102 is provided to take advantage of cooler temperature against window 80 for condensation, if valve 50 is set to route output air partially or entirely to outlet 106 instead of, or in addition to, outside outlet 83. The collected water can then be used for hydration, for example, by recycling the water through a line 105 back to the water source 32. Source gas may be provided from room air by means of valve 40. An optional valve 54 allows moist heated air from chamber 36 to be output within the room or other area after it has contacted the storage medium in the chamber 36 (not shown).

There are a number of options for providing heat storage medium 12. In one embodiment, chamber 36 is a replaceable canister or other easily removable container that can be used to generate heat for a room or other location. Once the canister has been hydrated and its stored heat obtained, the canister may be removed and returned to a recharging site at which dehydration takes place. This type of arrangement makes it possible, for example, to take advantage of higher energy sources than might be usable near human habitation or than might be available at the time and/or location of its use for generating heat. An example of such use would be to move the canister of hydrated storage medium 12 to a furnace area of a building for dehydration. When dehydration is complete, the canister can be brought back to a room for hydration and heat evolution. Such a replaceable canister may contain one or more trays or other support means for the storage medium 12.

Optional heating devices 44 a and 44 b used with embodiments of the present invention can use heat from any of a number of sources, in addition to heating elements. Waste heat from combustion, such as from a furnace, radiator, hot water heater, fireplace, stove, oven, clothes washer or dryer, or excess heat from a nuclear or industrial process can be used, for example. The heat used for heating the source gas 15 or for heating the heat storage medium 12 can be from a renewable source, such as solar thermal, geothermal, wind, or hydroelectric power, for example. Batteries and fuel cells can be used to generate heat, coupled with various types of resistive or thin-film heating devices. Another source of heat may be from the addition of water to anhydrous salts of calcium chloride, magnesium chloride, magnesium sulfate or sodium carbonate which may also be subsequently dehydrated for re-use, though under higher temperature conditions than those employed in the present invention.

EXAMPLES

In one embodiment of the present invention, heat storage medium 12 was, initially, fully hydrated sodium tetraborate decahydrate, commonly known as borax or with the alternative formula Na₂[B₄O₅(OH)₄].8H₂O, in a tray that was housed within an insulated container. Outdoor air at −7° C. and 80% relative humidity (RH) was brought through a conduit through a wall of a room that was at 9° C. and 61% relative humidity. The tubing was connected to the inlet of a blower that simultaneously heated the air. The outlet of the blower was connected to tubing, the end of which was placed at the bottom of the insulated container. The top of the container was partially open to allow air, with the added moisture from its dehydrating action on the hydrated salt, to leave the container.

The heated outdoor air moved through the container containing the tray of borax for about five hours, during which time the temperature of the borax had increased to about 48° C. After this time, the borax was found to have lost about 23% of its weight, indicating conversion of the borax from its original decahydrate to a composition having a similar empirical formula to sodium tetraborate pentahydrate. Addition of water to the dehydrated composition in a weight ratio of 1:3.2 at 22° C. resulted in a temperature rise of the hydrated sodium tetraborate to about 45° C. with a concomitant rise in the temperature and humidity of the air in the insulated container.

Another specific example of the present method with the above apparatus is similar to that just described, except that the tray in the insulated container contained partially hydrated sodium sulfate containing about 13% water, by weight. Dehydration was carried out with outdoor air that was at −7° C. and 80% RH brought by intermittent use of a blower, such that the blower did not heat the outdoor air, through a conduit through a wall of a room having indoor air at 9° C., 63% RH. With a heater in contact with a tray containing the partially hydrated sodium sulfate, the salt temperature rose to about 32° C., resulting in a weight loss of about 13% indicating conversion to predominantly anhydrous sodium sulfate. Addition of water to the dehydrated composition in a weight ratio of 1:5 at 19° C. resulted in a temperature rise of the hydrated sodium sulfate to about 25° C. with a concomitant rise in the temperature and humidity of the air in the insulated container.

Another specific example of the present method used magnesium sulfate heptahydrate, which was converted by dehydration to magnesium sulfate hexahydrate. This was accomplished using outdoor air at 2° C. and 88% RH. Continuous blowing and heating of this air through a conduit surrounded by indoor air at about 7° C. and 64% RH resulted in air entering the insulated chamber at about 55° C. and 2% RH. Additional heating was supplied by a heater in contact with the magnesium sulfate heptahydrate so that the salt temperature was about 45° C. After a short time the salt experienced a 7% weight loss, indicating conversion to a composition approximating magnesium sulfate hexahydrate. Further treatment under the same conditions resulted in a total weight loss of about 14%, indicating conversion to a composition with the empirical formula approximating magnesium sulfate pentahydrate.

An alternative batch method used to dehydrate magnesium sulfate heptahydrate was performed in which the magnesium sulfate heptahydrate was placed in a container with anhydrous calcium chloride. The air in the container was about 22° C. and 15% relative humidity prior to heating the magnesium sulfate heptahydrate in a tray with a heater. Upon heating the hydrated magnesium sulfate reached about 45° C. and was dehydrated to a composition approximating magnesium sulfate tetrahydrate as evidenced by a total weight loss of about 28%. In the absence of the calcium chloride, addition of water to this dehydrated sample in a weight ratio of about 1:3.6 at about 22° C. resulted in a temperature rise of the rehydrated magnesium sulfate to about 50° C. with a concomitant rise in temperature and humidity of the air in the container.

Another specific example of the present method with the above apparatus used partially hydrated sodium carbonate containing about 25% by weight water which was converted to predominantly sodium carbonate monohydrate. With intermittent use of the blower as described above for sodium sulfate, the salt temperature was about 30° C., with weight loss of about 13%. In this specific example, the outdoor air was 0° C. at 70% RH and the indoor air was about 10° C., 50% RH.

A further specific example of the present method was carried out using indoor air as the source gas at about 20° C. and about 20% RH. The air is heated by a hot water radiator that is part of a home heating system to about 40° C. and 5% RH, then is blown across a free standing tray holding sodium sulfate, partially hydrated with water to about 20% by weight, reaching a temperature of about 30° C. This resulted in about 20% weight loss from the partially hydrated sodium sulfate. Rehydration of this material by water addition in a weight ratio of 1 part water to 5 parts dehydrated sodium sulfate at about 20° C. led to a temperature rise of the rehydrated sodium sulfate to about 32° C.

Materials

Preferred materials for use as the storage medium are those that give off heat when exposed to water and are capable of releasing water at temperatures well below the boiling point of water when exposed to dry gas. Such materials include those that incorporate water into their crystal structures such as inorganic salts that form hydrates. Such materials include those having an equilibrium phase transition temperature in the range from above 30° C. to about 100° C., and preferably in the range of 30° C. to 85° C. Preferably, the hydrated forms of the salt or salts utilized are capable of efflorescence at moderate temperatures within the range from about 10° C. to about 70° C. or are capable of dehydration with the release of heat in this temperature range.

Included among these materials are hydrates listed in Table 1. The hydrated and dehydrated materials listed below may refer to empirical compositions that may be mixtures of thermodynamically stable hydrates or to the thermodynamically stable hydrates themselves. For example, magnesium sulfate tetrahydrate and pentahydrate, while described as products of efflorescence, may also each correspond to a mixture of magnesium sulfate hexahydrate and monohydrate in the respective appropriate ratio.

TABLE 1 Fully Potentiated and Fully Hydrated Forms of Salts Salt Preferred potentiated salt Preferred hydrated salt sodium sodium carbonate monohydrate sodium carbonate carbonate heptahydrate sodium anhydrous sodium sulfate sodium sulfate sulfate decahydrate sodium sodium tetraborate pentahydrate sodium tetraborate tetraborate decahydrate magnesium magnesium sulfate hexahydrate or magnesium sulfate sulfate magnesium sulfate pentahydrate or heptahydrate magnesium sulfate tetrahydrate

While these salts are among those preferred, compositions having other degrees of hydration may also be present in the potentiated and hydrated states of the process and both the preferred potentiated and preferred hydrated salts may be present at the same time. Any of a number of types of alternate materials that exhibit heat evolution upon hydration and loss of water upon exposure to dry gas can be used, including as hydrated forms of the materials, sodium thiosulfate pentahydrate or dihydrate; copper sulfate pentahydrate; zinc sulfate heptahydrate or hexahydrate; potassium aluminum sulfate dodecahydrate; trisodium phosphate dodecahydrate; disodium hydrogen phosphate dodecahydrate or heptahydrate; sodium dihydrogen phosphate dihydrate; tri-(sodium metaphosphate) hexahydrate; calcium chloride tetrahydrate; calcium acetate dihydrate; magnesium acetate tetrahydrate or mixtures thereof. Preferred salts are stable in the presence of water and air so that they are able to undergo a larger number of cycles without degradation in performance or formation of undesirable amounts of impurities.

The storage medium 12 can be formed so that it provides a favorable surface for energy transfer at a given rate. In one embodiment, for example, the medium is provided within chamber 36 as a canister, with the medium formed in a shape in which at least one dimension is small, such as for example, less than about 0.7 cm, and the other dimensions are longer, such as extending along the length and width of a canister, for example.

Liquid water is generally preferred for forming the hydrated salts, since it can help to release energy more quickly, thus providing a larger temperature increase of the storage medium 12 and not requiring use of added energy for vaporization, as would be needed to use water vapor. The water for water supply 32 can be from gravity or line feed and may be added in drop-wise or in continuous fashion.

The method and apparatus of the present invention overcomes the deficiencies of the methods and mechanisms heretofore proposed for a number of reasons, including at least the following:

-   1. Low temperature energy collection. In embodiments of the present     invention, heat energy may be efficiently absorbed and accumulated     with the hydrated salt at temperatures at or below its equilibrium     phase transition temperature. In one embodiment, such as when     furnace exhaust duct heat is used as a heat source for dehydration,     gas/air temperatures of the dry contacting gas are below about     100° C. throughout the process, more preferably below about 80° C.     throughout the process, even more preferably below about 65° C.     throughout the process. In another embodiment, such as when heated     room air from a radiator or forced air duct is used as a heat     source, dry contacting gas/air temperatures are maintained below     about 50° C. throughout the process. -   2. Reduced risk to humans in habitable areas. The heat energy is     used and/or stored in a medium at temperatures that are allowable in     close proximity to, or within, living areas. -   3. Location flexibility. Because the gas that is used to dehydrate     can originate from air as the source gas at or below about 20° C.,     the heat storage may take place at or near the same location to the     source of the gas and the heat may be used within a short time     period from the completion of the dehydration. -   4. Use of dry gas to dehydrate. After liberating the heat therefrom,     the storage medium may then be dehydrated again by subjecting it to     a dry gas. Heating of the storage medium with a heat source other     than the heated gas can help to speed the storage process, but is     optional. -   5. Indefinite number of cycles. This cycle of dehydration and heat     discharge may be repeated indefinitely. That is, the cycle of     hydration and dehydration itself does not limit the lifetime of heat     storage medium 12. Factors that can influence how many cycles are     feasible include the rate of loss of storage medium 12 over time and     rate of introduction of pollutants and impurities.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention as described above, and as noted in the appended claims, by a person of ordinary skill in the art without departing from the scope of the invention. Various methods could be used for drying the air or applied gas.

Thus, what is provided is an apparatus and method for more efficient accumulation, storage and controlled release of thermal energy and humidity.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Table of Reference Numbers 10. Hydration step 68, 70. Air input subsystem 12. Heat storage medium 76. Earth 14. Water 78. Air input subsystem 15. Source gas 80. Window 16. Contacting gas 81. Air input 18. Water vapor 82. Weather-stripping 20. Energy storage step 83. Air output 30. Gas filled area 84. Insulation 32. Water supply 90. Hollow circle 34. Valve 92. Filled circle 36. Chamber 94. Equilibrium phase boundary 40. Inside/outside source valve 96. Line 41. Desiccant canister 100. Bypass conduit duct 42. Blower 101. Direct/Bypass valve 44a. Heater for source gas 102. Condensation tank 44b. Heater for storage medium 103. Air outlet inside room 46. Humidity Sensor 104. Air inlet inside room 47. Room temperature and 105. Condensate line for recycling humidity sensors 106. Outlet 50. Valve 110. Air from bypass conduit into room 52. Filter 111. Contacting gas into room 54. Valve 112. Contacting gas exhausted outside 60. Air input subsystem 114. Chamber temperature sensor 62. Wall 115. Ambient air from room 64. Conduit 

1. A method of supplying heat to a gas filled space, comprising: a) adding a quantity of water to a dehydrated material in solid form that releases heat upon exposure to water, producing a hydrated material, b) exposing the hydrated material to dry contacting gas, releasing heat and water vapor from the hydrated material to the contacting gas and regenerating the hydrated material back to dehydrated material; and c) dispersing the heated contacting gas.
 2. The method of claim 1 further comprising: d) when at least a selected percentage of the water added in step (a) has been removed by exposure in step (b), repeating the method from step (a).
 3. The method of claim 2, in which the selected percentage is 85%.
 4. The method of claim 2, further comprising the step, before repeating, of removing any remaining water from the material by exposing the hydrated material to vacuum.
 5. The method of claim 1 further comprising: e) measuring the water vapor in the heated contacting gas from step (b) as the water vapor of the heated contact gas first increases, then reaches a peak value, then declines as the water is removed from the hydrated material; and f) when the water vapor of the heated contacting gas stops declining after it has begun decreasing, repeating the method from step (a).
 6. The method of claim 1, further comprising the step of removing heat from the hydrated material and dispensing the removed heat to the gas filled space by passing a gas through a conduit in thermal contact with the hydrated material.
 7. The method of claim 1, further comprising controlling humidity in the gas filled space by dispersing the heated contacting gas into the gas filled space to raise humidity and dispersing air from a conduit in thermal contact with at least one of the hydrated material or the heated contacting gas to maintain or lower humidity.
 8. The method of claim 7, in which the controlling is done by switching between a conduit carrying the heated contacting gas and a bypass conduit carrying gas from a source of gas, in thermal contact with at least one of the hydrated material or the heated contacting gas.
 9. The method of claim 1, further comprising the step of condensing at least a portion of the water from the contacting gas and recycling the condensed water as part of the water added in step (a) of claim
 1. 10. The method of claim 1, in which the material is contained in a chamber, and further comprising the step of contacting at least a thermally conductive portion of the chamber of the material with the source gas prior to step (b) of claim
 1. 11. The method of claim 1, in which the dry contacting gas is generated from a source gas by heating the source gas.
 12. The method of claim 1, further comprising the step of drying the source gas by contacting the source gas with a desiccant, resulting in a dry contacting gas.
 13. The method of claim 1, wherein the quantity of water added in step (a) is selected such that a percentage of the water and material mixture that is solid, by volume, is greater than 50% following the water addition.
 14. The method of claim 1, wherein the quantity of water added in step (a) is in a range of 5% to 50% of the dehydrated material by weight.
 15. The method of claim 1, wherein the quantity of water added in step (a) is in a range of 15% to 35% of the dehydrated material by weight.
 16. The method of claim 1, further comprising maintaining the material in step (b) at a temperature no higher than an equilibrium phase transition temperature of the hydrated material throughout the process.
 17. The method of claim 1, wherein water is added in step (a) at a rate of greater than 0.1 weight percent of dehydrated material per second.
 18. The method of claim 1, wherein water is added in step (a) at a rate of greater than 10 weight percent of dehydrated material per second.
 19. The method of claim 1 in which the hydrated material comprises one or more materials selected from a group consisting of magnesium sulfate heptahydrate, magnesium sulfate hexahydrate, magnesium sulfate pentahydrate, sodium carbonate decahydrate, sodium carbonate heptahydrate, sodium sulfate decahydrate, sodium tetraborate decahydrate, sodium thiosulfate pentahydrate, sodium thiosulfate dihydrate, copper sulfate pentahydrate, zinc sulfate heptahydrate, zinc sulfate hexahydrate, potassium aluminum sulfate dodecahydrate, trisodium phosphate dodecahydrate, disodium hydrogen phosphate dodecahydrate, disodium hydrogen phosphate heptahydrate, sodium dihydrogen phosphate dihydrate, tri-(sodium metaphosphate) hexahydrate, calcium chloride tetrahydrate, calcium acetate dihydrate and magnesium acetate tetrahydrate.
 20. The method of claim 1, in which the hydrated material has an equilibrium phase transition temperature in a range of 30° C. to about 100° C. 